A steerable wheel axle of the mentioned kind is known from WO-A 82/00983. There, a nondriven wheel axle for a fork lift is described, whose rigid axle body is pivotably suspended on the chassis. Considered with respect to a vertical, longitudinal median plane of the wheel axle, the axle body has an asymmetric shape, meaning that it has a convexity on one side. Inside this protruding portion, the axle body comprises a steering device, wherein a steering cylinder is arranged parallel to the longitudinal median axis of the wheel axle and receives a working piston. This cylinder is articulately connected at each of its ends via short steering tie rod segments with the steering arms of both wheels. This integration of the steering system in the axle body has the disadvantage of increased overall dimensions of the axle body and thus a weight increase of the wheel axle. The higher weight has an unfavorable effect on the overall construction of the vehicle and, when the wheel axle is provided with spring action, it has a negative influence on its dynamics during travel. Problems arise also from the steering kinematics of this system, since the short steering tie rods segments arranged between the steering arms and the ends of the working piston can lead to expanded positions of the articulatedly connected elements and to considerable steering angle errors.
Finally, it is not possible to develop a wheel axle built this way into a driven steering axle with a differential and with a driving shaft leading from this differential to the wheels, since, at least in the construction of the prior art, the steering system occupies the space required for the axle drive.
DE-AS 16 55 927 describes a servo-assisted steering device for a steerable wheel axle in which a push-rod system from a steering gear leads to the steering arm of a steering knuckle. The steering arms assigned to the two steering knuckles are connected via a continuous tie rod and power-assisted by hydraulic servocylinders. The arrangement of the servocylinders in the travel direction of the vehicle requires a lot of room and there is danger of damaging the servocylinders.